1. Field of the Invention
The present invention relates generally to a Hybrid Automatic Repeat reQuest (HARQ) system, and more particularly, to a HARQ method and apparatus for a system operating at least two cells.
2. Description of the Related Art
Mobile communication systems have evolved into high-speed, high-quality wireless packet data communication systems, such as, 3rd Generation Partnership Project (3GPP) High Speed Packet Access (HSPA) and Long Term Evolution (LTE), 3rd Generation Partnership Project 2 (3GPP2) High Rate Packet Data (HRPD), Ultra Mobile Broadband (UMB), and Institute of Electrical and Electronics Engineers (IEEE) 802.16e standard systems. These wireless packet data communication systems provide data and multimedia services beyond the early voice-oriented services.
As a representative broadband radio communication standard, LTE adopts Orthogonal Frequency Division Multiplexing (OFDM) in downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) in uplink.
In order to combat the occurrence of decoding failure at initial transmission, LTE adopts HARQ for retransmission of the decoding-failed data on the physical layer. HARQ is a technique in which, when decoding has failed, the receiver sends the transmitter a Negative Acknowledgement (NACK), enabling the transmitter to retransmit the decoding-failed data. If the data is decoded successfully, the receiver sends the transmitter an Acknowledgement (ACK), enabling the transmitter to send new data.